Millianism is reasonable; that is, it is reasonable to think that all there is to the semantic value of a proper name is its referent. But Millianism appears to be undermined by the falsehood of Substitutivity, the principle that interchanging coreferential proper names in an intentional context cannot change the truth value of the resulting belief report. Mary might be perfectly rational in assenting to ‘Twain was a great writer’ as well as ‘Clemens was not a great writer’. Her confusion does not seem to preclude her from assenting to those sentences in a normal, understanding manner. That is, Assent-for-Mary is true: Mary can knowingly assent to ‘Twain was a great writer’ and ‘Clemens was not a great writer’. By Disquotation—the rough principle that if in ordinary circumstances one assents to “P”, then one believes that P—Mary believes that Twain was a great writer and she believes that it’s not the case that Clemens was a great writer. If Substitutivity were true, then since ‘Mary believes that Twain was a great writer’ is true, ‘Mary believes that Clemens was a great writer’ would have to be true too. But then Mary would amount to a refutation of the plausible principle Consistency that, roughly put, no rational adult can have occurrently held and reflectively considered and compared contradictory beliefs. Since Disquotation, Assent-for-Mary, and Consistency are true, Substitutivity has to go.